Electrophotographic apparatus using photosensitive member with electrically high insulating layer

ABSTRACT

The disclosed photosensitive member comprises a supporting substrate, an electrode, a visible photoconductive layer and a thin layer of an electrically high insulating material which is transmissive to visible light, and is photoconductive in the ultraviolet range. The insulating layer is irradiated with visible light from an object to be reproduced and is simultaneously charged with a predetermined polarity through corona charging to form an electrostatic latent image corresponding to the object on the insulating layer. After the electrostatic image undeveloped or developed, has been transferred to a record medium, the electrostatic image left on the insulating layer is erased by irradiation with ultraviolet radiation.

United States Patent 11 1 Ohnishi et al. [4 1 Dec. 4, 1973 [54] ELECTROPHOTOGRAPHIC, APPARATUS 7 3,536,483 10/ I970 Watanabe et al 355/3 X 3,630,608 12/1971 Sage 355/17 X USING PHOTOSENSITIVE MEMBER WITH ELECTRICALLY I-IIGII INSULATING LAYER Inventors: Nasaru Ohnishi; Michi Yoshizawa,

both of Amagasaki, Japan Assignee: Mitsubishi Denki Kabushiki Kaisha,

Tokyo, Japan Filed: Nov. 13, 1972 Appl. No.1 305,827

Foreign Application Priority Data Nov. I6, 1971 Japan ..46/9l755 U.S. Cl 355/3, 355/17, 96/1 R, 346/74 ES Int. Cl G03g 15/00 Field of Search 355/3, 17; 96/1 R; 346/74 ES References Cited UNITED STATES PATENTS 4/197] Schlein et al. 355/3 Primary ExaminerRobert P. Greiner Attorney-E. F. Wenderoth et al.

[57] ABSTRACT The disclosed photosensitive member comprises a supporting substrate, an electrode, a visible photoconductive layer and a thin layer of an electrically high insulating material which is transmissive to visible light, and is photoconductive in the ultraviolet range. The insulating layer is irradiated with visible light from an object to be reproduced and is simultaneously charged with a predetermined polarity through corona charging to form an electrostatic latent image corresponding to the object on the insulating layer. After the electrostatic image undeveloped or developed, has been transferred to a record medium, the electrostatic image left on the insulating layer is erased by irradiation with ultraviolet radiation.

6 Claims, 5 Drawing Figures ELECTROPHOTOGRAPHIC APPARATUS USING PHOTOSENSITIVE MEMBER WITH ELECTRICALLY HIGH INSULATING LAYER BACKGROUND OF THE INVENTION This invention relates to an electrophotographic apparatus, and more particularly to such an apparatus employing a photosensitive member including an electrically insulating surface layer and utilizing the effect of dielectric polarization upon the photosensitive member.

There have been previously known photosensitive sheet-like members for use in electrophotographic processes which comprise the supporting substrate, electrode, photoconductive layer and thin'transparent layer of electrically high insulating material, superposed on each other in the named order and adapted to form a sustained electrostatic latent image on the insulating layer through the utilization of the effect of dielectric polarization on the high insulating andphotoconductive layers. These types of photosensitive members are described and claimed, for example, in U.S. Pat. Nos. 2,90l,348,3,04l,l67 and 3,055,006.

in order to form an electrostatic latent image on a photosensitive member of the type as above described, the following process is generally used: First while, for example, visible light uniformly irradiates the photosensitive member from the side of the high insulating layer, a corona charging is effected to uniformly charge that layer with one polarity. Subsequently the insulating layer thus charged is irradiated with a light image to be recorded and simultaneously another corona charging of opposite polarity is effected to form an electrostatic latent image corresponding to the light image on the surface of the high insulating layer. Finally the entire surface of the insulating layer is irradiated with visible light intense enough to remove a floating charge left in the interior of the underlaid photoconductive layer thereby to leave a pattern of polarized chargeon the surface of the photoconductive layer-and in opposite relationship with the electrostatic latent image. ln this way, the electrostatic latent image, stably sustained, is formed on the photosensitive member wit a small temporal change.

Therefore unlike the well-known F. Carlson process, it is not required to form and hold a desired electro-' static latent image on the surface of a photoconductive layer and then to erase any residual charge on that layer by irradiating the latter with light after the image has been developed and recorded. This has resulted in a great advantage in that the photoconductive layer can increase in photosensitivity by selecting the material therefor high in photosensitivity and low in resistivity,

' for example, cadmium sulfide (CdS) or seleniumtellurium (Se Te) compound.

n the other hand, the use of the photosensitive member with a high insulating layer has encountered problems in erasing any residual electrostatic image on the insulating layer before the succeeding operation of forming another electrostatic latent image on that layer. In order to prevent any residual electrostatic latent image from being developed in overlapping relationship with the succeeding electrostatic latent image, the insulating layer must be highly charged with a polarity reversed from that of the desired electrostatic latent image subsequently formed thereon, thereby to erase the residual image. To this end, a corona charging device involved has been required to be selectively connected to a pair of positive and negative voltage sources having a voltage as high as several thousand volts. Further with toner particles used for development, it is necessary to charge the insulating layer to erase any residual electrostatic latent image thereon after those toner particles not transferred to a record medium and remaining on the layer have been fully removed therefrom. In that event the toner particles are attracted to the residual electrostatic image by Coulomb forces developed therebetween, this leads to an additional disadvantage in that the cleaning operation i.e. removing the toner particles from the insulating layer is not facilitated.

SUMMARY OF THE INVENTION Accordingly it is an object of the present invention to provide a new and improved electrophotographic apparatus capable of readily erasing any electrostatic latent image to be recorded which is left on the electrically high insulating layer involved while retaining the advantages of the prior art practice.

It is another object of the invention to provide a new and improved electrophotographic apparatus simple in processing steps and excellent in characteristics by using an improved photosensitive member operatively associated with a corona charging device required only to be supplied by a single source of high voltage having its polarity determined by the conduction typev or the N or P type of the associated photoconductive layer.

It is another object of the invention to provide a new and improved electrophotographic apparatus for use with a dry development processes including means for simply removing toner particles left on a surface layer of a photosensitive member involved thereby decreasing reproduction time.

It is an additional object of the invention to increase the contrast or signal-to-noise ratio of reproduced images.

The present invention accomplishes these objects by the provision of an electrophotographic apparatus including a photosensitive member comprising a supporting substrate having at least one surface rendered photosensitive layer disposed on the conductive surface of the substrate and having a photosensitivity within a wavelength range of radiation ernitted from a light image to be reproduced, and a thin layer of insulating material disposed on the photoconductive, photosensitive layer, the insulating material being transmissive to radiation within the wavelengh range of the radiation from the light image, and means for irradiating the thin insulating layer with the radiation from the image to be reproduced and simultaneously electrically charging the insulating layer to form an electrostatic latent image corresponding to the light image on the surface of the thin layer. The present invention is further characterized in that, the insulating material is responsive to predetermined radiation outside the wavelength range of radiation from the light image to be reproduced, and is photoconductive. The invention is further characterized in that there is provided means for irradiating the thin layer with radiation of spectrum to which the thin layer is photoconductive, thereby to erase the electrostatic latent image on the thin layer.

Preferably, the photoconductive layer may be composed of a photoconductive material sensitive to visible radiation of spectrum and the insulating material of the thin layer may be sensitive to ultraviolet radiations of spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a fragmental perspective view of a photosensitive member for use with electrophotographic apparatus constructed in accordance with the principles of the prior art with some parts broken away;

FIG. 2 is a view similar to FIG. 2 but illustrating a photosensitive member constructed in accordance with the principles of the invention;

FIG. 3 is a schematic view of an electro-photographic apparatus constructed in accordance with the principles of the invention and utilizing a wet development process;

FIG. 4 is a view similar to FIG. 3 but illustrating a modification of the invention utilizing a dry development process; and

FIG. 5 is a schematic view of a modification of the arrangement shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and to FIG. I in particular, there is illustrated va conventional photosensitive member in the form of a sheet for use with electrophotographic apparatus. The photosensitive member is generally designated by the reference numeral and comprises a supporting substrate 12, a thin electrode 14 disposed on the substrate 12, a photoconductive layer 16 disposed on the electrode 14 and a thin layer of 18 disposed on the layer 16 to form a unitary structure. The electrode 14 may be of a thin layer of vacuum-deposited aluminum, or a carbon containing conductive material coated on one surface of the substrate 12 and the photoconductive, photosensitive layer 16, may consist of any suitable photoconductive material such as a powder of cadmium sulfide (CdS) and a binder such as cellulose nitride. Alternatively the layer 16 may be of any suitable photoconductive material vacuum-deposited on the electrode 14. Thin layer 18 is of any suitable transparent, electrically high insulating material such as polyester resin. Alternatively it may be a film commercially available under MY- LAR" (trade mark).

If desired, the electrode 12 may be a sheet of any photosensitive member 10 while light irradiates it from the side of the high insulating layer 18. If the photoconductive layer 14 is of an N type material, the photosensitive member 10 is positively charged. On the contary, if the photoconductive layer 14 is of a P type material, the member 10 is negatively charged. Assuming that the photoconductive layer 14 is of an N type material, the photosensitive member 10 has the exposed surface of the high insulating layer 18 uniformly charged with the positive polarity.

The second step or secondary charging step is to irradiate the photosensitive member 10 with a light image to be recorded in the same direction as in the first step while at the same time a corona charging is effected having its polarity opposite to that effected in the first step. That is, under the assumed condition, a negative corona charging is effected. Only for purposes of illustration, it is assumed that the light image to be recorded includes bright portions from which light from a light source is reflected to the photosensitive member and dark portion from which light from the source is not at all reflected to the photosensitive member. A positive charge at each point on the surface of the high insulating layer 18 due to the first step decreases by means of negative charge at that point due to the second step. Thus the quantity of charge left at each point on the insulating layer 18 is proportional to a ratio of impedance between those portions of the high insulating and photoconductive layers 18 and 16 respectively located below that point since the impedance of the photoconductive layer 16 is higher on the dark portions and lower on the bright portions, the quantity of negative charge developed on the surface of the high insulating layer 18 due to the secondary charging is smaller on the dark portions and greater on the bright portions. This causes the insulating surface to retain the positive charge on the dark portions and to be negatively charged on the brightportions. Thus the high insulating layer 18 forms on the surface thereof an electrostatic latent image consisting of positively and negatively charged portions corresponding in pattern to the light image.

Finally, the third step is to uniformly irradiate the entire surface of the high insulating layer 18 with sufficiently intense light. That is, the photosensitive member 10 is subject to the flood exposure. This flood exposure functions to remove a floating charge left in the interior of the photoconductive layer 14 to leave only the electrostatic latent image formed on the surface of the high insulating layer 18 having a high ability to re- 7 tain an electric charge thereon and a pattern of polarized charge developed on the surface of the photoconductive layer 14 in opposite relationship with the pattern of the electrostatic latent image. This yields the electrostatic latent image small in temporal change and therefore stable.

Then the electrostatic latent image thus formed on the surface of the high insulating layer 18 can be developed and recorded in accordance with any one of dry and wet development processes well known in the art.

The process of forming electrostatic latent images as above described has the disadvantages as previously described.

In order to eliminate those disadvantages, the present invention uses a photosensitive member such as shown in FIG. 2. The photosensitive member generally designated also by the reference numeral 10 in FIG. 2 comprises a supporting substrate 12 and an electrode 14 disposed thereon, the two being identical in construction to those shown in FIG. 1. The photosensitive member 10 further comprises a photoconductive layer 20 disposed on the electrode 14 and a thin layer 22 of electrically high insulating material disposed on the layer 20 to form a unitary structure as in the arrangement illustrated in FIG. 1.

The layer 20 is formed of any suitable photoconductive material having a photoconductivity within a wavelength range of radiation emitted from a light image to be recorded and preferably within the spectral range of visible radiation. As an example, the layer 20 may be prepared by mixing a cadmium sulfide (CdS) powder having added thereto a very small amounts of copper and chlorine with from 5 to 50 percent by volume of a binder selected from the group consisting of the vinyl, acrylic acid and cellulose systems. The material thus prepared is applied on the electrode 14 to a thickness of from 60 to 150 microns in any suitable manner. In the example illustrated, the material after having been formed into the layer 20 included 0.005 percent by weight of copper and 0.05 percent by weight of chlorine. The photoconductive layer 20 thus formed is responsive to the irradiation of visible light to decrease in its internal impedance.

n the other hand, the thin layer 22 is composed of any suitable electrically high insulating material having a photoconductivity outside the wavelength range of radiations from the light image and preferably within the spectral range of ultraviolet radiation to exhibit the photoconductive property. An example of the material of the layer 22 is polyvinyl carbazole containing about 0.2 percent by weight of picric acid and dissolved into a solvent such as dioxan, tetrahydrofran or the like. The solution thus prepared is applied to the photoconductive layer 20 in a thickness of about to 20 microns as by coating. The high insulating layer 22 formed of the material as above described normally has a resistivity of ohms-cm and is responsiveto ultraviolet ra-' diation incident thereupon to exhibit a resistivity of l0 ohms-cm or less.

The formation of an electrostatic latent image on the photosensitive member 10 of FIG. 2 is accomplished by only two steps simplified as follows:

A first step is to irradiate the photosensitive member 10 with that radiation stimulating the photoconductive high insulating layer 22, in this case, ultraviolet radiation being intense enough to sufficiently decrease the internal impedance of the'layer'22 t'o extinguish any used electrostatic latent image remaining on the surface of the layer 22. This results in the cleaning of the photosensitive member 10 and particularly of the surface of the layer 22.

The second step is to form the desiredelectrostatic latent image on the now cleaned surfaced of the photoconductive high insulating layer 22 of the photosensitive member 10. To this end, the photosensitive member 10 or the surface layer 22 thereof is irradiated with a visible light image of an. object to be copied such as a document, a picture, a drawing or the like while at the same time any suitable corona charging device is used to charge the member 10 with a predetermined polarity. For example, if the photoconductive layer is of an N type material, then the corona charging device is of a negative polarity as above described. If desired, it may be of a positive polarity. The visible light image is passed through the layer 22 to the photoconductive layer 20 to decrease the internal impedance thereof in a pattern conformed to the brightnesspattern of light image to permit the corresponding leakage of V the charge on the surface of the layer 22. As a result, an electrostatic latent image is formed onthe surface of the photoconductive high insulating layer 22 which image corresponds in pattern to the light image. That is, the latent image thus formed includes those portions charged positively and negatively with respect to the ground potential in accordance with the bright and dark portions of the light image.

Then the electrostatic latent image on the photosensitive member 10 is subject to development, transfer and fixation treatments well known in the manner.

Referring now to FIG. 3, there is illustrated an electrophotographic apparatus with the photosensitive member 10 of FIG. 2 constructed in accordance with the principles'of the present invention. The arrangement illustrated utilizes a wet development process and comprises an object 30 to be reproduced such as a document, a drawing or the like, and a lens 32 for focussing a beam of radiation, in this case, that portion of visible light from a light source (not shown) and reflected from the object 10 onthe exposed surface of the photosensitive member 10 or the surface of the photoconductive high insulating layer 22. When the photosensitive member 10 is being irradiated with the beam of light reflected from the object 10, any suitable corona charging device 34 is adapted to be moved toward and away from the photosensitive member 10 in the direction of the arrow A shown in FIG. 3 to form an electrostatic latent image corresponding in pattern to the object 30 on the surface of the photosensitive member 10 or of the photoconductive high-insulating layer 22 in the manner as above described.

Then the photosensitive member 10 having the electrostatic latent image formed thereon is displaced in the direction of the solid arrow B shown in FIG. 3 toward its position as illustrated at dotted block in the same Figure. During this displacement, the photosensitive member 10 is successively irradiated with a beam of light from an incandescent lamp 36 until the beam of light irradiates the whole surface of the photosensitive member 10 or its layer 22. This causes the erasure of any residual charge in the photoconductive layer 20 of the photosensitive member 10 resulting in an increase in the stability of the latent image retained on the surface of the high insulating layer 22.

On the other hand, an electrostatic record medium in the formof a dielectric coated tape from a supply roll 38 travels in the direction of the solid arrowC shown in FIG. 3 to pass under a' transferring roll 42 held at the ground potential or at a suitable potential reversed in polarity from the electrostatic latent image. The roll ,42 serves to put the adjacent portion of the dielectric coated tape 38 in pressure contact with the exposed surface of the photosensitive member 10 thereby to transfer the electrostatic latent image from that surface to the adjacent portion ofthe dielectric coated tape 38 by a transferring mechanism well known in the art.

The record tape 38 having the electrostatic latent image transferred thereto passes through a wet development unit 44 where it is developed in. a well known manner. Thereafter the tape 38 passes through a drier unit 46 for drying the tape with hot air. The dried portion including a reproduction of the object 30 of the I tape 38 reaches a cutter 48 where it is cutoff in a predetermined length whereuponthe reproduction is completed. v v

On the other hand, after the electrostatic latent image has been-transferred from the photosensitive member 10 to the dielectric coated tape 38, the photosensitive member 10'is returned back to the original position in the direction of the dotted arrow D shown in FIG. 3. During this return movement, a source 50 of radiation emitting that radiation stimulating the photoconductive property of the layer 22, in this case, an ultraviolet lamp 50 irradiates the entire surface of the layer 22 to render it electrically conductive thereby to erase the electrostatic latent image retained in the surface of the layer 22. At that time the apparatus has completed the operation of reproducing the object 30 and is ready for the succeeding reproducing operation.

FIG. 4 shows a modification of the present invention employing a dry development process. The arrangement illustrated includes a photosensitive drum 60 in the form of a cylinder having a cylindrical surface formed of a photosensitive member (not shown) as above described in conjunction with FIG. 2 and adapted to be rotated at a predetermined fixed speed in the direction of the arrow E or in the clockwise direction as viewed in FIG. 4. As in the arrangement shown in FIG. 3, a lens 32 focusses that portion of light beam from an incandescent lamp 62 reflected from an object 30 to be reproduced on the photosensitive surface of the rotating drum 60 after it has been transmitted through a corona charging device 34 substantially transmissive to the light beam from the object 30. In

that event there is provided means for driving the lens 32 or moving the object 30 in synchronization with the rotational movement of the photosensitive drum 60 whereby an electrostatic latent image is successively formed corresponding in pattern to a light image resulting from the object 30. Only for purposes of illustration, such means is not shown in FIG. 4.

As the drum 60 is rotated, the electrostatic latent image thereon is moved past an incandescent lamp 36 to be stabilized as in the arrangement of FIG. 3. Thereafter, that portion of the drum 30 having formed thereon the electrostatic latent image enters a dry development unit 64 where the latent image is developed with toner particles disposed therein in the well known manner.

During a further rotational movement of the drum 60, a transferring roll-42 is operated to transfer the developed image from the drum to a dielectric coated tape 38 from a supply roll 40 in the similar manner as above described in conjunction with FIG. 3 excepting that the toner particles attached to the electrostatic image on the drum 30 are directly transferred to the record tape 38 without transferring the electrostatic image itself.

Then the tape 38 with the transferred image enters a fixation unit 46 where it is fixed by heating, after which a cutter 48 cuts off the tape 38 into a predetermined length. At that time, the reproduction of the object has been completed.

On the other hand, the drum 60 continues to be rotated in the direction of the arrow E shown in FIG. 4. During this rotational movement, the photosensitive surface of the drum 60 is successively irradiated with a ultraviolet lamp 50 so that any residual electrostatic image is erased. Then a wiper wheel 68 serves to remove the toner particles still attached to the'drum surface. Thus the photosensitive drum 60 is ready for the succeeding operation.

Then the process as above described can be repeated with the same or different object.

The arrangement as shown in FIG. 4 is advantageous in that an object even through it would be long, can be continuously reproduced. It will readily be understood that elec trophotographic apparatus using the wet development process such as shown in FIG. 3 may readily be modified to perform the continuously reproducing operation.

In order to improve the contrast or signal to noise ratio of reproductions, the photosensitive member of the present invention can be preferably subject to the primary charging treatment as above described in conjunction with the prior art type process before an electrostatic latentimage will be formed thereon. FIG. 5 shows a modification of the invention in which reproductions formed are improved in contrast. In FIG. 5, an incandescent lamps and another corona charging device 72 are shown as being added to the arrangement of FIG. 3. In the arrangement illustrated, the photosensitive member 10 is first caused to reciprocate between its position shown at the solid block and its position directly below the lamp and charging device 70 and 72 vertically aligned with each other. During this reciprocating movement, the photosensitive member 10 is uniformly irradiated by the incandescent lamp 70 while being uniformly charged by the corona charging device 72. Under these circumstances, if the photoconductive layer 20 is of ,an N type material then the corona discharger 72 is of a positive polarity and the corona charging device 34 is of a negative polarity.

After having been charged with the corona charging device 72, the photosensitive member 10 is moved from its position as shown at the solid block in FIG. 4 and initiated to be processed in the manner as above described in conjunction with FIG. 3. It is noted that in the arrangement of FIG. 3, the surface of the photoconductive layer 22 is at the ground potential while in the arrangement of FIG. 5 that surface is charged with the polarity opposite to that of an electrostatic latent image formed thereon. This results in an increase in the contrast of reproductions formed.

It will readily be appreciated that the incandescent lamp and corona charging device 70 and 72 respectively may be advantageously added to the arrangement of FIG. 4.

It is known that the polyvinyl carbazole as above de scribed has only a low sensitivity to ultraviolet radiation in its inactivated state and can be' imparted with a sensitivity to radiation lying in a wide range of from ultraviolet radiations to visible radiations, by having added thereto an appropriate sensitizer. For example, H. Hoegl's article, Journal of Physical Chemistry, Vol. 69, No. 8 (1965) pp 755-766 describes that polyvinyl carbazole can be combined with nitro-compounds, picric acid or the like to control photosensitivity. Also it is possible to impart to polyvinyl carbazole photosensitivity only in the ultraviolet range by adding a suitable additive to it, for example, picric acid.

The present invention has been described in tenns of polyvinyl carbazole having added thereto 0.2 percent by weight of picric acid. If picric acid in a smaller amount is added to polyvinyl carbazole its photosensitivity to ultraviolet radiations decreases. That is, it decreases in reduction in internal impedance in response to the irradiation of ultraviolet radiations. Therefore, any residual electrostatic image on the surface of the layer 22 formed of such polyvinyl carbazole can not be sufficiently discharged to be erased. 0n the contrary, an increase in an amount of picric acid added to polyvinyl carbazole results in the resulting layer 22 having a reduced time interval in which it can retain a potential. In addition, it is sensitive to ultraviolet and visible radiation.

For those reasons it is necessary to select an amount of picric acid to be added to polyvinyl carbazole dependent upon the magnitude of impedance of the associated photoconductive layer 20 and the intensity of ultraviolet radiation required to erase the electrostatic image on the surface of the layer 22 etc. Also the thickness of the layer 22 should be selected in accordance with magnitudes of impedance of the visible photoconductive layer 20 when it is irradiated and when it is not irradiated with visible radiation. It has been found that in the arrangements as above described, the layer 20 has a thickness of from 5 to 20 microns with satisfactory results.

Examples of the material for the ultraviolet photoconductive, insulating layer 22, in addition to the polyvinyl carbazole sensitized with 0.2 percent by weight of picric acid, are polyvinyl compounds such as polyvinyl pyrene, polyvinyl anthracene etc. and zincic compounds such as zinc xide(ZnO), zinc sulfide'(ZnS), zinc sulfide-cadmium sulfide(ZnS-CdS) mixture etc.

Examples of visible photoconductive layer 20 and sintered films of cadmium sulfide(CdS), vacuum deposited films of selenium-tellurium system, films of sensitized zinc oxide (ZnO), films of cadmium sulfide-zinc sulfide(CdS-ZnS) system, films of cadmium sulfidecadmium selenide(CdS-CdSe) system, etc.

If desired, polyvinyl carbazole may be formed into a two layer structure including a surface layer having a photoconductivity in the ultraviolet range and a lower layer having a photoconductivity in the visible range of spectrum. Then the surface layer provides the insulating layer 22 while the lower layer provides the photoconductive layer 20.

ln the arrangementsillustrated, the photoconductive insulating layer 22 has been described as formed of a photoconductive material having a photosensitivity in the ultraviolet range of spectrum. However it is to be understood that the material of the layer 22 is not restricted to such photosensitive material and that the layer 22 may be effectively formed of any suitable photoconductive material having no photosensitivity in a range of radiations used in the operation of forming electrostatic latent image and having a photosensitivity in a range of radiations other than that range.

While the invention has been illustrated and described in conjunction with a few preferred embodiments thereof it is to be understood that numerous changes and modifications may be resorted to without departing from the spirit and scope of the invention.

What we claim is: 1. An electrophotographic apparatus comprising in combination, a photosensitive member comprising a supporting'sub strate having at least one surface rendered electrically conductive, a photoconductive layer disposed on the conductive surface of said substrate and having a photosensitivity within a wavelength range of radiation emitted from a light image to be reproduced, and a thin layer disposed on said photoconductive layer and formed of an electrically high insulating material which is transmissive to radiation within said wavelength range of radiation from said light image and is photoconductive to predetermined radiation outside said wavelength range, means for irradiating said insulating layer with said radiation from said light image and simultaneously electrically charging said insulating layer to form an electrostatic latent image corresponding to said light image on the surface of said insulating layer, and means for irradiating said insulating layer with radiation to which said insulating layer is photoconductive thereby to erase the electrostatic latent image.

2. An electrophotographic apparatus as claimed in claim 1, wherein said radiation from said light image is substantially visible radiation and said radiation to which said insulating layer responds is substantially ultraviolet radiation.

3. An electrophotographic apparatus as claimed in claim 2, wherein said thin layer is formed of polyvinyl carbazole having added thereto picric acid.

4. An electrophotographic apparatus as claimed in claim 2, wherein the material of said thin layer is selected from the group consisting of polyvinyl pyrene and polyvinyl anthracene.

5. An electrophotographic apparatus as claimed in claim 2, wherein the material of said thin layer is selected from group consisting of zinc oxide and zinc sulfide.

6. An electrophotographic apparatus as claimed in claim 1, further comprising another means for uniformly charging the surface of said thin layer with a polarity opposite to the polarity with which said means uniformly charges the surface of said thin layer while irradiating the surface of said photoconductive insulating layer. 

2. An electrophotographic apparatus as claimed in claim 1, wherein said radiation from said light image is substantially visible radiation and said radiation to which said insulating layer responds is substantially ultraviolet radiation.
 3. An electrophotographic apparatus as claimed in claim 2, wherein said thin layer is formed of polyvinyl carbazole having added thereto picric acid.
 4. An electrophotographic apparatus as claimed in claim 2, wherein the material of said thin layer is selected from the group consisting of polyvinyl pyrene and polyvinyl anthracene.
 5. An electrophotographic apparatus as claimed in claim 2, wherein the material of said thin layer is selected from group consisting of zinc oxide and zinc sulfide.
 6. An electrophotographic apparatus as claimed in claim 1, further comprising another means for uniformly charging the surface of said thin layer with a polarity opposite to the polarity with which said means uniformly charges the surface of said thin layer while irradiating the surface of said photoconductive insulating layer. 